Tracked vehicle with improved track drive unit

ABSTRACT

An all-terrain vehicle is supported and driven by endless track units. Each track unit includes a drive belt with rows of interior drive lugs driven by cogs on multiple sprocket wheels of a common drive wheel assembly having an integrated, one-piece drum and hub. Multiple guide wheel assemblies engaging the lower run of the drive belt distribute the vehicle load across substantially the full width of the belt. Each guide wheel assembly includes a pair of guide wheel units mounted on opposite end portions of a common spindle and on opposite sides of a carrier beam of the track unit. Each guide wheel unit has a wide belt-engaging surface extending to, or close to, an edge portion of the belt and interrupted by an annular groove permitting passage of a row of the belt drive lugs while maintaining alignment of the belt and drive wheel assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/666,028, filed Sep. 17, 2003 now U.S. Pat. No. 6,983,812,which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to all-terrain tracked vehicles, and moreparticularly to an improved endless drive track unit for such trackedvehicles.

BACKGROUND OF THE INVENTION

Endless track-driven vehicles are commonly used off-road in difficultterrain and under difficult terrain conditions, such as in mud, snow,sand, and tundra. For example, tracked vehicles are used in snow countryfor grooming ski slopes and snow mobile trails, for transporting skiersto back-country slopes, for ski resort maintenance work, and for snowand mountain rescue. They are also used in various types of terrain forutility company maintenance work, and for oil exploration and oilpipeline maintenance in arctic tundra.

Tracked vehicles are generally of two types. Many are two-tracked inwhich a pair of endless drive track units, one on each of the oppositesides of the vehicle, support and drive the vehicle. Others arefour-tracked, in which four separately driven and independentlysuspended drive track units, two in front and two in the rear, supportand drive the vehicle.

Four-tracked vehicles have certain advantages over two-tracked vehiclesunder extreme conditions such as on steep slopes and in very roughterrain because of the flexible independent suspensions of the trackdrive units and the constant power available to all of the track driveunits, even while turning. Unlike a two-tracked vehicle which relies onthe differential speed of the two tracks for turning, a four-trackedvehicle steers much like a wheeled vehicle. Its endless drive trackunits can be physically turned for steering.

In many tracked vehicles, such as the four tracked vehicles shown inU.S. Pat. No. 6,007,166, the lower, ground-engaging run of the track hasbeen supported by a plurality of single-element guide wheels disposedsubstantially inline longitudinally of the track and generally engagingonly a centralized region of the track. Although this system, with asingle line or row of guide wheels, functioned adequately, it was foundthat substantial deflection of the track on opposite sides of the guidewheels was occurring. This deflection was caused generally by thehigh-point loading of the track by the guide wheels at the center of thelateral dimensions of the track. This could lead to premature failure ofelements in the track due to high cyclical stresses. This samehigh-point loading of the track and its consequential deflection couldalso lead to premature failure of the track and reduce its effectivetraction. The high-point loading of the track was also transmittedthrough the track to the underlying terrain. In the case of sensitiveterrain such as tundra, such loading could cause excessive damage to theterrain, especially with the endless track usually including tractionbars or cleats on its outer surface for enhancing the vehicle'straction.

The drive track unit disclosed in U.S. Pat. No. 6,129,426, addressed theforegoing problems by providing guide wheel assemblies along the lowertrack run, with each assembly including multiple guide wheels mounted ona common guide wheel hub. This increased the guide wheel surface contactarea across the width of the track, thereby reducing point loading ofthe track and consequential track deflection and wear, as well asterrain damage. Although this was a substantial improvement over theprior art and alleviated the aforementioned problems to some extent, itdid not do so altogether. Consequently, some of the track wear andterrain disturbance problems still occurred, especially with all-terrainvehicles that carry heavy loads. Despite there being three separatewheel rims mounted on a common hub, there still remained essentiallyonly a single wheel unit in each such guide wheel assembly, and thesurface contact areas of the three rims with the track were stillrelatively small compared to the overall width of the track. Therefore,each such single three-wheel guide wheel assembly still left extensiveoutwardly and inwardly extending track surface areas across the width ofthe track unsupported on the lower track run. Accordingly, substantialtrack deflection and wear could still occur, as could substantial damageto sensitive terrain underlying the track area.

Another problem with the guide wheel assemblies of the track units ofU.S. Pat. No. 6,129,426, was that such guide wheel assemblies were notprovided throughout the entire lower track run of the track unit. It wasstill necessary to include at least one single guide wheel along thelower track run, to provide clearance for the drive wheel assembly ofthe track unit. Thus, single point loading of the track still occurredalong at least a portion of the lower track run.

Furthermore, the drive track units of some prior all-terrain vehicles,especially four-tracked vehicles intended for use on sensitive terrain,have had endless tracks comprising one-piece, endless, molded rubberbelts, as disclosed in both of the aforementioned U.S. Pat. Nos.6,129,426 and 6,007,166, each with rows of inwardly extending hardrubber drive lugs positioned on the inner circumference of the belt.These lugs engaged and meshed with drive cogs on a drive sprocket wheelassembly of the drive track unit. Heretofore, such drive sprocket wheelassemblies have been expensive to fabricate and assemble because oftheir multiple separate parts. Such parts have included separatesprocket wheels bolted to a common sprocket drum, which in turn wasbolted to an axle hub. The hub in turn, was bolted to an end flange ofthe drive axle itself. The resulting drive wheel assembly was also quiteheavy and, especially when used in multiples in a four-tracked vehicle,added substantial weight to the vehicle, thereby increasing the loadingof its often already heavily loaded drive tracks.

In the past, drive track units with rubber drive belts have alsoincluded outer, ground-engaging surfaces with molded hard rubbertraction bars or cleats to improve traction. However, such cleats tendto exacerbate the ground disturbance problems arising from point- orconcentrated loading of the belts by the guide wheels of such units.

Another problem that can arise with drive track units that support heavyloads and utilize rubber drive belts, is that the belts may stretch or“give” in use especially when high driving forces are applied by asprocket wheel to the drive lugs of the belt. Such stretch can give riseto so-called track bounce creating heavy vehicle vibrations, or eventrack jump, where the belt lugs jump from engagement with the sprocketdrive cogs, causing the vehicle to lose power.

SUMMARY OF THE INVENTION

There is a need for an improved drive track unit for endlesstrack-driven vehicles, and especially for four-tracked vehicles and suchvehicles that carry heavy loads, that will overcome the foregoingproblems. It is therefore a general object of the present invention toprovide a track-driven vehicle that overcomes the foregoing problems andprovides improved traction, improved track wear, and less terraindisturbance than prior such vehicles, especially when carrying heavyloads.

Another object of the invention is to provide an improved drive trackunit for an all-terrain vehicle that is especially suited for heavyvehicles, and provides a better load distribution to the drive trackthan prior such assemblies, thereby reducing track damage and wear, andconsequential ground disturbance during use, and improving vehicletraction, while reducing the likelihood of track bounce or track jump.

A further object of the invention is to provide an improved guide wheelassembly for the drive track unit of a tracked vehicle that provides abetter load distribution to the drive track than prior such assembliesby mounting separate guide wheel units of the assembly on opposite sidesof a carrier beam of the drive track unit, thereby distributing thevehicle load across substantially the full width of the drive track, toreduce drive track damage and wear, and terrain disturbance, and improvevehicle traction.

Another object of the present invention is to provide a novel andimproved guide wheel assembly for the drive track unit of a trackedvehicle, with the assembly including drive wheel units that includerelatively wide track support surface portions that extend to, oradjacent to, the inner and outer edge portions of the drive track toreduce point-loading of the track, track deflection and wear, and grounddisturbance.

Yet another object of the invention is to provide an improved guidewheel unit for a guide wheel assembly of a drive track unit for atracked vehicle, such guide wheel unit having a relatively widetrack-engaging surface provided with an annular groove that allows forthe free passage of drive lugs of a supported endless track through suchgroove, while providing improved guidance of the track along the lowertrack run.

Another object of the invention is to provide an improved drive trackunit for a tracked vehicle, including a series of guide wheel assembliesspaced along the lower track run all of which support and distribute thevehicle load to the drive track across substantially the full width ofthe track excepting where rows of drive lugs of the track pass the guidewheels of the assemblies.

Another object of the invention is to provide an improved drivesprocket-and-belt drive for a belt-driven drive track unit of anall-terrain vehicle, including an improved drive lug arrangement on thebelt and improved drive cog arrangement on the drive sprocket assemblyto reduce belt and sprocket wear, reduce the possibility of track bounceand track jump, and improve power transmission from the sprocket wheelassembly to the drive belt.

Another object of the invention is to provide an improved drive trackunit for an all-terrain vehicle, including an endless drive belt that iswider and provides better traction with less terrain disturbance thanprior such drive belts.

A further object of the invention is to provide an improved drive wheelassembly for the drive track unit of an all-terrain vehicle in which theassembly is of simplified construction, lower cost, and lesser weightthan prior such assemblies by providing an integrated one-piece driveaxle hub and sprocket drum for connecting multiple drive sprocket wheelsto a drive axle of the unit.

The foregoing and other objects, features, and advantages of theinvention will become more apparent from the following detaileddescription which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a four-tracked, all-terrain vehiclehaving four separate and independently suspended and driven drive trackunits, each with an endless drive track, guide wheel assemblies, and adrive wheel assembly in accordance with a preferred embodiment of theinvention;

FIG. 2 is an enlarged side elevational view of an endless drive trackunit shown in FIG. 1;

FIG. 3 is a top plan view of the drive track unit of FIG. 2 with theendless drive belt removed;

FIG. 4 is a perspective view of the drive track unit of FIG. 2;

FIG. 4A is a perspective view similar to FIG. 4, but with the drive beltremoved from the drive track unit;

FIG. 5 is a vertical sectional view taken along the line 5—5 of FIG. 2showing details of the drive wheel assembly and its mounting to thetrack unit frame;

FIG. 5A is a view similar to FIG. 5, but showing an alternativeembodiment of the drive sprocket wheel assembly and drive belt of thedrive track unit of the invention;

FIG. 6 is a vertical sectional view taken along the line 6—6 of FIG. 2showing the details of construction of a guide wheel assembly and itsmounting to the frame of the drive track unit;

FIG. 7 is an elevational and partial sectional view of a guide wheelassembly of the invention taken along the line 7—7 of FIG. 3 showing howthe wheel spindle of a guide wheel assembly is mounted to the carrierbeam of a drive track unit.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

To provide a comprehensive disclosure without unduly lengthening thespecification, applicant incorporates herein by reference thedisclosures of U.S. Pat. Nos. 6,129,426, 6,007,166, 3,787,099, and3,857,616.

Referring first to FIG. 1, a four-track all-terrain vehicle 10 has avehicle body 12 supported by four identical endless drive track units14, 16, 18, and 20, respectively. Track units 14 and 20 are mounted atopposite sides of the rear of the vehicle, and track units 16, 18 aremounted at opposite sides of the front of the vehicle. Each drive trackunit is independently mounted, driven, and steerable in a well-knownmanner. At the forward end of the vehicle, a snow plow, grader blade, ora variety of other attachments (not shown) may be mounted. Similarly,various attachments may be mounted at the rear end of the vehicle, allfor multiple operations over a variety of terrain. The particularvehicle shown includes a load platform 13.

Referring to FIGS. 2–6, one of the track units 16 is illustrated ingreater detail. The track unit includes a horizontal carrier beam 24extending lengthwise of the drive track unit and connected to thevehicle body through a frame structure or carrier assembly 26 secured toan axle tube 28 mounted to the chassis of vehicle body 12. A series offour longitudinally spaced-apart guide wheel assemblies 30 and a drivewheel assembly 32 are mounted to support an endless drive track in theform of rubber drive belt 34 in a generally triangular configuration.Drive wheel assembly 32 is mounted at the apex of the triangle, andguide wheel assemblies 30 are spaced apart along the base of thetriangle defined by the lower track run 34 a of drive belt 34. The fourguide wheel assemblies 30 are of identical size and construction andspaced apart along the carrier beam 24 such that none of them interferewith the drive wheel assembly 32 or the carrier assembly 26 that mountsit to the carrier beam.

As shown best in FIGS. 2 and 3, carrier beam 24 includes opposite endportions 24 a, 24 b that telescope into main carrier beam member 24 c.Threaded length adjustment members 25 a, 25 b interconnect the oppositeend portions 24 a, 24 b, with main carrier beam member 24 c to providefor adjustment of the overall length of carrier beam 24. Thus, byadjusting the length of carrier beam 24, the amount of tension appliedto the drive belt 34 by the end-most guide wheel assemblies 30 can beadjusted.

As shown best in FIGS. 2, 3, and 5, drive wheel assembly 32 is drivinglyconnected to drive axle shaft 40 and rotatably supported by the outerend portion of axle tube 28. Axle shaft 40 includes an axle shaftextension 38 at its outer end that is rotatably supported by an endplate 36 of the carrier assembly. Axle tube 28 in turn is supported byan upwardly extending portion 26 a of carrier assembly 26. An axle tubemounting member 42 secures the axle tube 28 to carrier portion 26 a. Anoutwardly extending portion 26 b of carrier assembly 26 includes athreaded adjustment member 27. Together they serve as a carrier stopassembly to limit oscillation of the carrier assembly and thus the drivetrack unit, about drive axle shaft 40 in a well known manner throughengagement with a leaf spring (not shown) on the chassis.

Referring especially to FIG. 5, drive wheel assembly 32 is rotatablydriven by the powered axle 40 extending through axle tube 28. Drivewheel assembly 40 includes an integrated one-piece hub-and-sprocket drum44 rotatably supported on the outer end portion of axle tube 28 bybearings 46. The integrated hub-and-drum 44 is drivingly connected to aflanged end portion 48 of axle shaft 40. Generally radially extendingflanged opposite end portions 50, 52 of the integrated hub-and-drum 44mount a pair of sprocket wheels 54 a, 54 b in axially spaced apartrelationship to form a gap 56 therebetween.

Each sprocket wheel 54 a, 54 b is bolted to a different one of theintegrated hub/drum flanges 50 a, 50 b by bolted connections at 52 a, 52b, respectively, at the inner rims of the sprocket wheels.

Each sprocket wheel 54 a, 54 b includes a plurality of circumferentiallyspaced-apart cogs 58 at its outer circumference. In the preferredembodiment, each cog is an integral part of its sprocket wheel andextends laterally inwardly and outwardly from the central disc portionof the wheel. Each laterally extending portion of each cog 58 forms asprocket tooth for drivingly engaging drive lugs in a row of such lugson the endless drive belt, as explained further below. The integratedone-piece construction of the hub-and-drum 44 greatly simplifies theconstruction, manufacture, and assembly of the drive wheel assembliesand their installation in the drive track units, and results in areduction in the overall weight of the drive track units, and thus thevehicle.

Referring to FIGS. 2, 4, and 5, the endless drive belt 34 includes asmooth, flat outer surface 60 to minimize ground disturbance, but has awidth that extends across the full width of the guide wheel assemblies30, as shown best in FIG. 5, to minimize terrain disturbance and yetprovide a large surface area contact with the ground and therefore goodtraction. The inside surface of the belt is provided with four laterallyspaced-apart rows of drive lugs 62 including a first row 62 a, a secondrow 62 b, a third row 62 c, and a fourth row 62 d. These lugs are moldedin place and preferably constructed of hard rubber. The lugs in each roware circumferentially spaced apart along the inside surface of the belt,and each such row is positioned to be drivingly engaged by a set ofdrive cogs 58 extending laterally from one side of one of sprocketwheels 54 a or 54 b.

Although the separate inside rows of drive lugs 62 b and 62 c arelaterally spaced apart, these two inside rows could be combined, ifdesired, into a single continuous row of wide lugs as shown in FIG. 5A,to add a stiffening effect to drive belt 34. Also, although belt 34 hasa smooth outer surface as previously described, it could be providedwith traction bars or cleats molded into the belt and extendinglaterally across the outside of the belt, if desired for increasedtraction and especially if terrain disturbance is not a concern. Such acleated belt is disclosed, for example, in the aforementioned U.S. Pat.No. 6,129,426, incorporated herein by reference.

Now referring especially to FIG. 6, each guide wheel assembly 30 alongthe lower track run, and therefore in engagement with drive belt 34,includes a pair of guide wheel units 64 a, 64 b, rotatably mounted atopposite end portions of a wheel spindle 66. The wheel spindle extendslaterally a substantial distance beyond each of the opposite sides ofcarrier beam 24 such that the guide wheel units 64 a, 64 b are mountedone on each of the opposite sides of the carrier beam. Wheel spindle 66is fixedly mounted to the carrier beam at the mid-portion of the spindleby a spindle clamp 68. As shown in FIG. 7, spindle clamp 68 includes anupper wheel spindle clamp seat 70 welded to carrier beam 24 and aspindle clamp cap 72 bolted to the clamp seat 70. Together, the spindleclamp and seat clamp wheel spindle 66 securely to the carrier beam. Aswill be apparent from FIG. 6 as well as FIGS. 4 and 5, the guide wheelassembly extends across substantially the full width of endless drivebelt 34.

Each wheel unit 64 a, 64 b of guide wheel assembly 30 includes a wheelhub 74 rotatably mounted to an outer end portion of wheel spindle 66 onbearings 76. Attached to the axially opposite ends of hub 74 are a pairof axially spaced-apart rigid metal rings including an outer ring 78having a wide rim 80 and an inner ring 82 having a much narrower outerrim 84. Each such ring is bolted to a flange portion of wheel hub 74 bybolts 86, 88. Each rim 80, 82 of a wheel unit is covered with anelastomeric outer covering including a wide outer covering 90 for thewide rimmed wheel ring 78 and a much narrower covering 92 for the narrowrimmed wheel ring 82. These outer coverings may be of a rubber orpolyurethane material to provide cushioning between the wheel assemblyand endless drive belt 34. The outer covering 90 of the wide rimmedwheel ring 78 extends inwardly and downwardly beyond wide wheel rim 80into a gap between the wide and narrow rimmed wheel rings to define anannular groove 94 separating the wide and narrow wheel rings. As clearlyshown in FIG. 6, groove 94 is sized to receive and allow clear passageof the outermost row of drive lugs 62 a of belt 34.

The innermost wheel unit 64 b is of identical size and construction tothe wheel unit 64 a such that the groove 94 of the inner wheel unitreceives the innermost row of drive lugs 62 d along the lower track runof belt 34.

It will also be noted that the spacing between outer wheel unit 64 a andinner wheel unit 64 b on wheel spindle 66 is such that the two wheelunits are not only spaced laterally from carrier beam 24 to which theyare mounted by the spindle, but are also spaced a sufficient distanceapart to allow clear passage of the two central rows of drive lugs 62 b,62 c. It will be apparent from FIG. 6 that, if desired, the two rows oflugs 62 b, 62 c can be combined to provide a single row of wide drivelugs. Such wide lugs would serve the same function as the two rowsshown, but would also provide additional stiffening for the drive belt34. It should also be noted that the four rows of drive lugs 62 a–62 dserve to resist any tendency of the drive belt 34 to shift laterallyrelative to the drive wheel assemblies. Thus, the drive lugs also serveas belt guide lugs.

From the foregoing, it will be apparent that each guide wheel assemblyextends across substantially the full width of the drive belt 34,thereby preventing any substantial deflection of the belt relative tothe guide wheel assemblies. Moreover, the pairs of guide wheel units ofeach guide wheel assembly, including their wide track support surfaces90 and narrower track support surfaces 92 provided by the elastomerwheel unit coverings, actually engage and support the drive belt acrosssubstantially the full width of the belt except for the two annulargrooves and spacing between wheel units that provide for unobstructedpassage of the belt lugs. Accordingly, point loading of the belt and itsattendant problems and disadvantages are substantially eliminated by theguide wheel assemblies of the present invention. Moreover, with suchwide distribution of the vehicle load across the drive belt, the load isalso distributed widely to the ground underlying the drive belt, therebyreducing substantially ground disturbance during vehicle travel.Furthermore, the wide distribution of the load across the drive belt tothe ground improves traction and thereby, in many cases, shouldeliminate the need for traction cleats on the outer surface of the belt,further reducing ground disturbance.

In summary, both belt wear and ground disturbance should be reduced withthe track units of the present invention because of the lighter weightof the drive wheel assemblies and better load distribution to the drivetracks of such units. Although the present invention has been describedherein with reference to what are currently preferred embodimentsthereof, it should be apparent to those skilled in the art thatvariations and modifications of the invention are possible withoutdeparting from the true spirit and scope of the present invention.

ALTERNATIVE PREFERRED EMBODIMENT

Referring to FIG. 5A, an alternative preferred embodiment of the drivetrack units 14–18, described with reference to FIGS. 1–7, includes thedrive track unit 14 a including a modified drive track belt 34 a andmodified drive wheel assembly 32 a. Other major components of the drivetrack unit remain substantially unchanged and as heretofore described.

Drive track belt 34 a includes three rows of integral drive lugs,including an outer row of lugs 62 e, a middle row of lugs 62 f, and aninner row of lugs 62 g. The drive lugs 62 e, 62 g of the outer and innerrows are sized to fit within and pass freely through the annular grooves94 of their respective outer and inner guide wheel units 64 a, 64 b.However, the lugs 62 f of the middle row are much wider than the lugs 62e, 62 g of the outer and inner rows. Lugs 62 f are sized to spansubstantially the full distance between the outer and inner guide wheelunits 64 a, 64 b of each guide wheel assembly.

The wide drive lugs serve two purposes. First, the wide lugs reinforceand add lateral stiffness to the belt to provide wear resistance andhelp maintain the belt in the track run. Second, the wide lugs, whencoupled with drive sprocket cogs of corresponding length, as describedbelow, provide a more efficient transmission of power from the drivesprocket wheel assembly 32 a to the drive belt 34 a by reducing pointloading of the lugs, thereby reducing even further the possibility oftrack bounce and track jump, and their consequences, and also reducingtrack and sprocket wear.

Drive sprocket wheel assembly 32 a is of the same general constructionas previously described sprocket wheel assembly 32 as shown in FIG. 5.However, the sprocket wheels 54 a, 54 b of drive wheel assembly 32 a areprovided with drive cogs 58 a having inward extensions 55 that extendinwardly from their respective sprocket wheels a greater distance thantheir outward extensions 57. The inward cog extensions 55 of the pair ofsprocket wheels 54 a, 54 b meet midway between such sprocket wheels.Thus, the inward cog extensions 55 of each pair of sprocket wheels 54 a,54 b drivingly engage the middle row of drive lugs 62 f of drive belt 34a across the full width of such lugs, thereby reducing the point loadingof the belt and therefore the possibility of track bounce and trackjump.

Another feature of drive belt 34 a is its greater width relative to theguide wheel assemblies 30, compared to the width of belt 34 relative toguide wheel assemblies 30 of FIG. 5. For example, whereas the widths ofthe guide wheel assemblies and belt in the embodiment of FIG. 5 may eachbe approximately twenty-six inches, the width of the wider belt 34 a inFIG. 5A may be approximately thirty inches for the same twenty-six inchwidth of guide wheel assembly 30, with belt 34 a extending approximatelytwo inches beyond the inner and outer limits of the guide wheelassemblies. The extra wide belt 34 a provides greater traction and lessterrain disturbance than would a narrower belt. Such advantages can beachieved without sacrificing any appreciable belt stability because ofthe enhanced belt stability provided by the described wide guide wheelassemblies, wide belt drive lugs, and improved power transmission fromthe drive sprocket wheel assembly to the drive belt.

In summary, both belt wear and ground disturbance should be reduced withthe track units of the present invention because of the lighter weightof the drive wheel assemblies and better load distribution to the drivetracks of such units. Although the present invention has been describedherein with reference to what are currently preferred embodimentsthereof, it should be apparent to those skilled in the art thatvariations and modifications of the invention are possible withoutdeparting from the true spirit and scope of the present invention.

1. A track-driven all-terrain vehicle comprising: a vehicle bodyportion; multiple drive track units supporting the body portion; each ofsaid drive track units including: a track frame, including a carrierbeam extending longitudinally of said vehicle; a powered rotatable trackdrive wheel assembly supported on said frame; plural guide wheelassemblies mounted on said carrier beam and in spaced apart relationshipalong said beam; an endless track trained about said drive wheelassembly and said guide wheel assemblies and being drivingly engaged bysaid drive wheel assembly and supported during ground engagement by saidguide wheel assemblies; each said guide wheel assembly including a wheelspindle fixedly mounted to said carrier beam and extending a substantialdistance laterally inwardly and outwardly beyond said carrier beam, anouter guide wheel unit rotatably mounted on an outwardly extendingportion of said wheel spindle, and an inner guide wheel unit rotatablymounted on an inwardly extending portion of said wheel spindle such thatsaid outer and inner guide wheel units are axially spaced apart onopposite sides of the carrier beam and define the width of saidassembly; said endless track comprising a drive belt extending laterallybeyond opposite sides of said carrier beam and having multiple laterallyspaced-apart and circumferentially extending rows of drive lugsextending inwardly from an inner surface of said belt, said multiplerows including at least one row on each of the opposite sides of saidcarrier beam; said drive wheel assembly comprising a sprocket wheelmeans including drive cogs for drivingly engaging drive lugs in all ofsaid multiple rows simultaneously, including said rows on opposite sidesof said carrier beam; and said inner and outer guide wheel units of saidguide wheel assemblies each including outer track support surfaces thatsupport substantially the full width of said drive belt except wheresaid rows of drive lugs are positioned.
 2. The vehicle of claim 1wherein each said guide wheel assembly extends substantially the fullwidth of said drive belt.
 3. The vehicle of claim 1 wherein the width ofeach said guide wheel assembly is substantially equal to and coextensivewith the width of said drive belt.
 4. The vehicle of claim 1 whereinsaid outer guide wheel unit of said guide wheel assembly supports anouter edge portion of said drive belt.
 5. The vehicle of claim 1 whereinsaid inner guide wheel unit of said guide wheel assembly supports aninner edge portion of said drive belt.
 6. The vehicle of claim 1 whereinsaid multiple drive track units comprise four said units.
 7. The vehicleof claim 6 wherein said drive wheel assembly and said guide wheelassemblies of each drive track unit support said drive belt in agenerally triangular configuration with said drive wheel assembly at theapex of said configuration and said guide wheel assemblies spaced apartalong the base of said configuration.
 8. The vehicle of claim 7 whereinthe width of each said guide wheel assembly is substantially equal toand coextensive with the width of said drive belt.
 9. A vehicleaccording to claim 1 wherein said drive belt includes at least threerows of drive lugs, and said drive cogs drivingly engage a drive lug ineach of said rows simultaneously.
 10. A vehicle according to claim 9wherein said at least three rows includes at least one row between therows on opposite sides of the carrier beam.
 11. A vehicle according toclaim 1 wherein the width of each guide wheel assembly is substantiallycoextensive with the width of said drive belt.
 12. A vehicle accordingto claim 1 wherein at least the forwardmost and rearwardmost guide wheelassemblies of said multiple guide wheel assemblies each has an overallwidth that is substantially coextensive with the width of said drivebelt.
 13. The vehicle of claim 1 wherein each of said inner and outerguide wheel units of each guide wheel assembly is provided with anannular belt-engaging surface and an annular groove sized to permitpassage therethrough of one of said rows of lugs and to maintain lateralalignment of said belt with said guide wheel assemblies.
 14. A vehicleaccording to claim 1 wherein said sprocket wheel means of said drivewheel assembly includes a pair of axially spaced apart sprocket wheels,each including cogs drivingly engaging a different one of said at leastone row of drive lugs.
 15. A vehicle according to claim 14 wherein thecogs of each one of said pair of sprocket wheels drivingly engage saidlugs of at least two of said multiple rows simultaneously.
 16. A vehicleaccording to claim 1 wherein all said guide wheel units of all saidplural guide wheel assemblies are of the same size and configuration.17. A vehicle according to claim 16 wherein said multiple drive trackunits comprise four said drive track units, each said drive track unitincluding four said guide wheel assemblies, each of said guide wheelassemblies including two said guide wheel units, and the guide wheelunits of all said guide wheel assemblies of all said drive track unitsbeing of the same size and configuration, such that the guide wheelunits of all said guide wheel assemblies are interchangeable.
 18. Avehicle according to claim 17 wherein each said guide wheel unitincludes an annular belt-engaging surface and an annular groovesubdividing said annular surface into laterally outer and inner surfaceportions, said annular groove being sized to permit passage therethroughof one of said rows of lugs and to maintain lateral alignment of saidbelt with said guide wheel assemblies.
 19. A vehicle according to claim18 wherein said outer surface portion of each said guide wheel unit iswider than said inner surface portion.
 20. The vehicle of claim 1wherein each drive track unit includes a drive axle, and each said drivewheel assembly includes a unitary one-piece drive axle hub and sprocketdrum directly and drivingly connected to said drive axle and to saidsprocket wheel means.
 21. The vehicle of claim 20 wherein said sprocketwheel means includes multiple sprocket wheels mounted in axiallyspaced-apart relationship on said sprocket drum.
 22. The vehicle ofclaim 21 wherein said multiple sprocket wheels comprise a pair of drivesprocket wheels directly and drivingly connected to opposite endportions of said unitary hub and drum.
 23. The vehicle of claim 22wherein each said sprocket wheel includes circumferentially spaced-apartdrive cogs extending laterally from opposite sides of the sprocket wheelfor drivingly engaging substantially the full widths of said drive lugsin said multiple rows.
 24. A track-driven all-terrain vehiclecomprising: a vehicle body portion; multiple drive track unitssupporting the body portion; each of said drive track units including: atrack frame, including a carrier beam extending longitudinally of saidvehicle; a powered rotatable track drive wheel assembly supported onsaid frame; plural guide wheel assemblies mounted on said carrier beamand in spaced apart relationship along said beam; an endless tracktrained about said drive wheel assembly and said guide wheel assembliesand being drivingly engaged by said drive wheel assembly and supportedduring ground engagement by said guide wheel assemblies; each said guidewheel assembly including a wheel spindle fixedly mounted to said carrierbeam and extending laterally inwardly and outwardly beyond said carrierbeam, an outer guide wheel unit rotatably mounted on an outwardlyextending portion of said wheel spindle, and an inner guide wheel unitrotatably mounted on an inwardly extending portion of said wheel spindlesuch that said outer and inner guide wheel units are axially spacedapart on opposite sides of the carrier beam and define the width of saidassembly; said multiple drive track units comprising four said units;said drive wheel assembly and said guide wheel assemblies of each drivetrack unit supporting said endless track in a generally triangularconfiguration with said drive wheel assembly at the apex of saidconfiguration and with said guide wheel assemblies spaced apart alongthe base of said configuration; said drive track comprising a drive beltincluding an inner surface having multiple circumferentially extendingrows of drive lugs extending inwardly therefrom, and said drive wheelassembly including multiple spaced-apart sprocket wheels includinglaterally extending drive cogs for drivingly engaging simultaneouslydrive lugs in all of the said rows of drive lugs; and said multiple rowsof drive lugs including at least one row positioned on each of theopposite sides of said carrier beam.
 25. The vehicle of claim 24 whereinsaid drive belt includes a smooth outer ground-engaging surface.
 26. Thevehicle of claim 24 wherein said guide wheel assemblies and said drivebelt are substantially coextensive in width.
 27. The vehicle of claim 24wherein said drive belt extends outwardly of the laterally outer limitsof said guide wheel assemblies.
 28. The vehicle of claim 24 wherein saidmultiple rows of drive lugs include a single row of drive lugspositioned between said inner and outer guide wheel units of said guidewheel assemblies, the width of the lugs of said single row beingsubstantially coextensive with the spacing between said inner and outerwheel units.
 29. The vehicle of claim 28 wherein said drive cogs includecog portions that drivingly engage substantially the full width of thelugs of said single row.
 30. The vehicle of claim 24 wherein each drivetrack unit includes a drive axle, and each said drive wheel assemblyincludes a unitary one-piece drive axle hub and sprocket drum directlyand drivingly connected to said drive axle, said multiple spaced-apartsprocket wheels being mounted in axially spaced-apart relationship onsaid one-piece drive axle hub and sprocket drum.
 31. A track-drivenall-terrain vehicle comprising: a vehicle body portion; multiple drivetrack units supporting the body portion; each of said drive track unitsincluding; a track frame, including a carrier beam extendinglongitudinally of said vehicle; a powered rotatable track drive wheelassembly supported on said frame; plural guide wheel assemblies mountedon said carrier beam and in spaced apart relationship along said beam;an endless track trained about said drive wheel assembly and said guidewheel assemblies and being drivingly engaged by said drive wheelassembly and supported during ground engagement by said guide wheelassemblies; each said guide wheel assembly including a wheel spindlefixedly mounted to said carrier beam and extending laterally inwardlyand outwardly beyond said carrier beam, an outer guide wheel unitrotatably mounted on an outwardly extending portion of said wheelspindle, and an inner guide wheel unit rotatably mounted on an inwardlyextending portion of said wheel spindle such that said outer and innerguide wheel units are axially spaced apart on opposite sides of thecarrier beam and define the width of said assembly; said multiple drivetrack units comprising four said units; said drive wheel assembly andsaid guide wheel assemblies of each drive track unit supporting saidendless track in a generally triangular configuration with said drivewheel assembly at the apex of said configuration and with said guidewheel assemblies spaced apart along the base of said configuration; saiddrive track comprising a drive belt including an inner surface havingmultiple circumferentially extending rows of drive lugs extendinginwardly therefrom, and said drive wheel assembly includes multiplespaced-apart sprocket wheels including laterally extending drive cogsfor drivingly engaging the said rows of drive lugs; and each of saidinner and outer guide wheel units of each guide wheel assembly beingprovided with an annular belt-engaging surface and an annular groovesized to permit passage therethrough of one of said rows of lugs and tomaintain lateral alignment of said belt with said guide wheelassemblies.
 32. A track-driven all-terrain vehicle comprising: a vehiclebody portion; multiple drive track units supporting the body portion;each of said drive track units including; a track frame, including acarrier beam extending longitudinally of said vehicle; a poweredrotatable track drive wheel assembly supported on said frame; pluralguide wheel assemblies mounted on said carrier beam and in spaced apartrelationship along said beam; an endless track trained about said drivewheel assembly and said guide wheel assemblies and being drivinglyengaged by said drive wheel assembly and supported during groundengagement by said guide wheel assemblies; each said guide wheelassembly including a wheel spindle fixedly mounted to said carrier beamand extending laterally inwardly and outwardly beyond said carrier beam,an outer guide wheel unit rotatably mounted on an outwardly extendingportion of said wheel spindle, and an inner guide wheel unit rotatablymounted on an inwardly extending portion of said wheel spindle such thatsaid outer and inner guide wheel units are axially spaced apart onopposite sides of the carrier beam and define the width of saidassembly; said drive wheel assembly and said guide wheel assemblies ofeach drive track unit supporting said endless track in a generallytriangular configuration with said drive wheel assembly at the apex ofsaid configuration and with said guide wheel assemblies spaced apartalong the base of said configuration; said drive track comprising adrive belt including an inner surface having multiple circumferentiallyextending rows of drive lugs extending inwardly therefrom, and saiddrive wheel assembly including multiple spaced-apart sprocket wheelshaving drive cogs for drivingly engaging simultaneously drive lugs inall of said multiple rows; and said multiple rows of drive lugsincluding at least one outer row positioned laterally outwardly of saidcarrier beam, at least one inner row positioned laterally inwardly ofsaid carrier beam, and at least one row positioned between said outerand inner rows.
 33. The vehicle of claim 32 wherein said drive beltincludes a smooth outer ground-engaging surface.
 34. The vehicle ofclaim 32 wherein each drive track unit includes a drive axle, and eachsaid drive wheel assembly includes a unitary one-piece drive axle huband sprocket drum directly and drivingly connected to said drive axle,said multiple spaced-apart sprocket wheels being mounted in axiallyspaced-apart relationship on said one-piece drive axle hub and sprocketdrum.
 35. A track-driven all-terrain vehicle comprising: a vehicle bodyportion; multiple drive track units supporting the body portion; each ofsaid drive track units including; a track frame, including a carrierbeam extending longitudinally of said vehicle; a powered rotatable trackdrive wheel assembly supported on said frame; plural guide wheelassemblies mounted on said carrier beam and in spaced apart relationshipalong said beam; an endless track trained about said drive wheelassembly and said guide wheel assemblies and being drivingly engaged bysaid drive wheel assembly and supported during ground engagement by saidguide wheel assemblies; each said guide wheel assembly including a wheelspindle fixedly mounted to said carrier beam and extending laterallyinwardly and outwardly beyond said carrier beam, an outer guide wheelunit rotatably mounted on an outwardly extending portion of said wheelspindle, and an inner guide wheel unit rotatably mounted on an inwardlyextending portion of said wheel spindle such that said outer and innerguide wheel units are axially spaced apart on opposite sides of thecarrier beam and define the width of said assembly; said drive wheelassembly and said guide wheel assemblies of each drive track unitsupporting said endless track in a generally triangular configurationwith said drive wheel assembly at the apex of said configuration andwith said guide wheel assemblies spaced apart along the base of saidconfiguration; and said drive track comprising a drive belt including aninner surface having multiple circumferentially extending rows of drivelugs extending inwardly therefrom, and said drive wheel assemblyincludes multiple spaced-apart sprocket wheels including laterallyextending drive cogs for drivingly engaging the said rows of drive lugs;each of said inner and outer guide wheel units of each guide wheelassembly being provided with an annular belt-engaging surface and anannular groove sized to permit passage therethrough of one of said rowsof lugs and to maintain lateral alignment of said belt with said guidewheel assemblies.
 36. The vehicle of claim 35 wherein said guide wheelassemblies and said drive belt are substantially coextensive in width.37. The vehicle of claim 35 wherein said drive cogs include cogsdrivingly engaging lugs in all of said rows simultaneously.